1. Field of the Invention
The present invention relates to a tomographic imaging apparatus and a tomographic imaging method, and more particularly, to a tomographic imaging method and a tomographic imaging apparatus which are used for ophthalmologic diagnosis and treatment.
2. Description of the Related Art
Currently, there are used various types of ophthalmologic apparatus using an optical instrument. Examples of the optical instrument for observing an eye include an anterior ocular segment photographing device, a fundus camera, and a confocal scanning laser ophthalmoscope (SLO). Of those, an optical tomographic imaging apparatus employing optical coherence tomography (OCT) which utilizes a low coherence beam is an apparatus capable of acquiring with a high resolution a tomographic image of an object to be inspected, and is thus becoming an indispensable apparatus as the ophthalmologic apparatus in outpatient treatment specialized in retina. Hereinbelow, this apparatus is referred to as OCT apparatus.
The OCT apparatus can measure cross-sections of an object to be inspected by splitting a low coherence beam into a reference beam and a measuring beam, irradiating the object to be inspected with the measuring beam, and causing interference to occur between a return beam from the object to be inspected and the reference beam. In other words, by scanning the object to be inspected with the measuring beam, a two-dimensional or three-dimensional tomographic image can be acquired. However, in a case where the object to be inspected is a living body such as an eye, movement of the eye causes a problem of image distortion. Thus, it is required that a high-sensitivity measurement be executed with high speed.
As one method for achieving this, U.S. Patent Publication No. 2008/0284981 discloses a method of simultaneously measuring a plurality of points of an object to be inspected. According to this method, by splitting a beam from a single light source, a plurality of beams is generated. Then, those beams are split by a beamsplitter into a plurality of measuring beams and reference beams, respectively. The object to be inspected is irradiated with the measuring beams, and return beams from the object to be inspected and the reference beams are combined by the beamsplitter. Then, the plurality of combined beams is caused to enter a grating, and resultant beams are simultaneously detected by a two-dimensional sensor. In this manner, U.S. Patent Publication No. 2008/0284981 attempts to achieve high speed by executing a simultaneous measurement using the plurality of measuring beams.
In the case where a plurality of points is simultaneously measured, depending on the apparatus configuration, the initial condition of the optical system needs to be measured in advance. Specifically, the apparatus has various tolerances, and hence, in some cases, a plurality of points cannot be measured under a desired condition. For example, there occurs a case where the measured area of each beam is displaced on a plane perpendicular to the optical axis, or there occurs a case where the measured area of each beam is displaced with respect to the optical axis direction (depth). If a measurement is executed without any consideration of such cases, a desired area cannot be measured.